This invention relates to a gas laser device having electrodes of improved construction.
An axial-flow gas laser is usually provided with a gas feed port at one end of a cylindrical discharge tube, and a gas outlet port at the other end thereof, and a gas medium is supplied from the feed port to the outlet port via the interior of the discharge tube. A mixed gas consisting of carbon dioxide (CO.sub.2), nitrogen (N.sub.2) and helium (He) is used as the gas medium. When the glow discharge is formed between an anode and a cathode provided in the discharge tube, an inverted population occurs in the gas medium to generate laser beams. The laser beams resonate between the reflector and output mirror provided at both ends of the discharge tube, to be taken out from the output mirror. There is a gas laser device, which has been developed with a view to improving a laser beam output, and which uses a cathode having a bore therein, i.e. a so-called ring-shaped cathode which is disclosed in U.S. Pat. No. 4,331,939. In the ring-shaped cathode, the glow discharge is formed uniformly on an inner surface of the bore therein to prevent the cathode from being locally overheated.
When the capacity of a gas laser generator is increased to a high level, for example, not less than 5-20 kW, it is necessary that the diameters of the discharge tube and cathode be increased to a great extent. Consequently, a large current is necessarily supplied to the cathode, so that the temperature of the cathode increases locally. As a result, the cathode is overheated locally, and arc discharge occurs. This makes it impossible to use the cathode practically.
Further, in the discharge tube of larger diameter than a certain diameter, for example 65 mm, the current density of glow discharge is not made uniform by a conventional cathode. Therefore, even if the large-sized discharge tube with a corresponding cathode is employed for making the capacity of a gas laser larger, the capacity does not increase corresponding to the scale of the discharge tube and the cathode.